Recent years, various electronic devices such as personal computers and mobile telephones have been reduced in size in accordance with the advance of the semiconductor technology. As the downsizing of the electronic devices proceeds, there have been attempts of using fuel cells as the power for the small-sized devices. The fuel cell can generate electrical power simply by supplying a fuel and an oxidizer thereto, and has such an advantage that it can continuously generate the electrical power by replacing the fuel. Because of such an advantage, the fuel cell, if it can be reduced in size, is considered to be an extremely useful system for driving mobile electronic devices. In particular, a direct methanol fuel cell (DMFC) is a promising power source for small-sized devices since it uses methanol, which has a high energy density and can be easily handled as compared to the hydrogen gas fuel, and electrical current can be obtained from methanol on an electrode catalyst without requiring any reforming instrument.
There are several methods of supplying fuel to a DMFC, for example, a gas-supply type DMFC in which liquid fuel is gasified and fed into the fuel cell with a blower or the like, a liquid-supply DMFC in which liquid fuel is fed into the fuel cell with a pump, and an internal gasifying type DMFC in which liquid fuel is gasified within the fuel cell. Of these, the internal gasifying type DMFC requires no large-scale equipments such as pump or blower for supplying the fuel. Therefore, the concentration of the liquid fuel is increased and the liquid fuel tank can be reduced in size, it becomes possible to achieve the realization of a small-sized fuel cell having a high energy density.
It should be pointed out here that Jpn. Pat. Appln. KOKAI Publication No. 2004-311163 discloses an improvement of the performance of a cell, which can be achieved by regulating the density of an organic compound component (formic acid, acetic acid or oxalic acid) contained in a catalyst layer of an electrode of the fuel cell.